For example, Japanese Patent Application Laid-Open Publication No. 2010-278814 (Patent Document 1) discloses a method of determining a broadcast domain by a service instance identifier (ISID) in a PBB network. Specifically, in each switching device in a PBB network, a correspondence relation between a service instance identifier (ISID) and a port corresponding thereto is retained in a table, by which a broadcast domain for each service instance identifier (ISID) is determined.